1. Field of the Invention
The present invention relates to an apparatus and method for switching a voice codec [e.g. speech codec] of a mobile terminal and, more particularly, to an apparatus and method for allowing an origination mobile terminal to select the same type voice codec as that of a destination mobile terminal and transmitting and receiving voice data through the selected voice codec to perform a voice call between different mobile communication systems.
2. Description of the Related Art
Currently, as mobile terminals are increasingly used, diverse supplementary functions can be performed by mobile terminals. In particular, the rapid advancement of a multimedia function of mobile terminals allows the mobile terminals to support reproducing of various formats of audio files.
Diverse voice codecs are currently provided and each codec is used in respective application fields according to its characteristics. A vocoder that determines basic call quality uses a different type voice codec for each mobile communication system, so in case of a voice call between different communication systems, a communication network must transcode a voice bit stream which has been encoded by a different codec so that vocoders of the different communication systems can exchange voice.
FIGS. 1A to 1C show the construction of a voice codec apparatus for a voice call of a general mobile communication system. Specifically, FIG. 1A shows the construction of a voice codec apparatus of general CDMA (Code Division Multiple Access) terminals, FIG. 1B shows the construction of a voice codec apparatus of general GSM (Global System for Mobile communication) terminals, and FIG. 1C shows the construction of a general voice codec apparatus for a voice call between different mobile communication systems.
With reference to FIG. 1A, a CDMA origination terminal 10 converts analog voice data into 64 kbps digital data through a PCM (Pulse Code Modulation), encodes the 64 kbps digital data into 8 kbps or 13 kbps data through a QCELP (Qualcomm Code Excited Linear Prediction) method (in case of PCS (Personal Communication System) or an EVRC (Enhanced Variable Rate Coder) method (in case of cellular system), and then transmits it. Then, a CDMA destination terminal decodes the 8 kbps or 13 kbps voice data according to the QCELP or the EVRC method, PCM-demodulates the decoded voice data and provides it to a user.
With reference to FIG. 1B, a GSM origination terminal 30 AMR (Adaptive Multi-rate)-encodes the PCM-demodulated voice digital data and transmits it. Upon receiving the AMR-encoded voice data, a GSM destination terminal 40 decodes the received voice data through the AMR, demodulates the decoded voice data through the PCM and then provides it to the user.
For example of a voice call between different mobile communication systems, as shown in FIG. 1C, in case of a voice call between the CDMA terminal of the CDMA system and the GSM terminal of the GSM system, since a voice codec of the CDMA system and that of the GSM system are different, a communication network performs a transcoding function to interface the voice codes of the two systems.
In other words, when the CDMA origination terminal 10 and the GSM destination terminal 40 performs a voice call, the CDMA origination terminal 10 encodes PCM-modulated voice data according to the QCELP or the EVRC method and then transmits it. Then, the communication network 50 decodes the voice data, which has been encoded according to the QCELP or the EVRC method, according to the QCELP or the EVRC method, encodes the decoded voice PCM data through the AMR, namely, the voice codec method of the GSM system, and then transfers it to the GSM destination terminal 40. Then, the GSM destination terminal 40 AMR-decodes the AMR-encoded voice data, demodulates the AMR-decoded voice data through the PCM, and provides the demodulated voice data to the user.
In the general voice call method between the different communication systems, when the communication network receives the voice data transmitted from the origination terminal, it decodes the received voice data by using the same voice codec as that of the origination terminal, encodes the voice data by using the same voice codec as that of the destination terminal, and then transmits it to the destination terminal. Accordingly, a load is applied to perform the transcoding of the communication network, the voice data can be damaged as it is decoded and encoded repeatedly on the channel, and a look-ahead delay for encoding is repeatedly generated.